The background of the present invention is the fact that the requirements on the setting accuracy of the profile of a metal strip, at least in predetermined strip width positions or so called reference positions, are constantly being increased, as are the requirements on the dimensional accuracy of the profile contour of the metal strip. Depending on the intended field of application for a metal strip, for example warm profile contours provided with a parabolic shape are expected to have a predetermined profile height in a predetermined reference position in order to simplify further processing downstream in a cold rolling mill (tandem line). As an alternative, box profiles may be also required, which is to say that metal strips with a flat cross-section in the center are required which is decreasing towards the band edges; this requirement is applicable for example to strip profiles are later to be divided in the longitudinal direction. On the other hand, concave strip profiles, in particular strip profiles having thicker or raised edges in comparison to their central region, or metal strips with an edge bead, are usually not desirable.
In order to make it possible to produce profiles that are as precise as possible, several approaches have been already proposed according to prior art.
So for example, the International Patent Application WO 1995/034388 discloses a detection system for detecting the profile of a metal strip at the exit of a finishing rolling line. The strip profile K detected therein is compared to a predetermined target profile and the use of profile actuators is proposed in order to minimize deviations of the measured profile from the subsequent strips.
Furthermore, a decision is also made as to whether the measured band profile form is acceptable or not, and other measures are proposed, for example a measure to change the thermal crown form of the working rollers in order to improve the profile form as required.
Document EP 0 618 020 B1 also aims to adapt the profile of a metal strip at the exit of a hot rolling strip line to a predetermined target contour. Mechanical actuators are used for this purpose so that a potentially determined deviation between a calculated, which is to say a projected strip form and a predetermined target contour is minimized. Also, a measured strip profile C40 is used (in the position 40 mm from the strip edge), in order to correct or set the control system.
Accordingly, a forecast value for the strip is provided and the setting values for the profile actuators during the rolling of an nth metal strip in a predetermined reference position are simulated and calculated with the aid of a mathematical and physical process model. The simulation is optionally carried out by taking into account the restrictions and the application of different profile actuators. After the rolling of the nth metal strip has been carried out, an adaptation value is calculated based on the difference between said forecast value and a measured actual value of the strip profile of the nth metal strip in said reference position. The reference position is measured at a predetermined strip width position from the natural edge of the metal strip, corresponding for example to 25 or 40 mm According to prior art, said forecast value and said adaptation value are determined or predetermined only with only a single reference position in order to define on this basis individual specifications for the strip profile.